Radio-transmitter for frequency-shift telegraphy made operative in response to modulation



Aug. 25, 1959 R, BOURGONJON ETAL 2,901,598

RADIO-TRANSMITTER FOR FREQUENCY-SHIFT TELEGRAPHY MADE OPERATIVE INRESPONSE TO MODULATION Filed May 5, 1954 lNvENToR Y LoulsRAYMQNDWBOURGONJON JOHANNES sANDwlJK AGENT kUnited States Patent-,.0 f'

sda; assgoraty messe ass grimms, ,fof Nanni American Philips Company,Inet.; New York',N'..,; a'f corporation of- Delaware applicaties May s,1s'szfgsefrst1ss. inist claims priority, applicationI Netherlands Mayis', 195s- 1 Crater. (Ci. zsolmr) This invention relates toradiLtrn's'mitters' for frequency-shift telegraphy and has for' itsobject to provide a transmitter of such constructiony as to be operativeonly on the occurrence of a train of tclegr-aphy pulses.l to betransmitted. Y

For this purpose, according to the inventions snclr, a radio-transmittercomprises a switching device Vwhich blocks at least one `of Vthe*transmissiony stages and c o-mprises al grid-controlled switch tube anda switch voltage generator, the latter comprising an input resistor,provided in the control-grid circuit of the switch tube, and a holdingcapacitor connected in series with a series resistor, to which capacitorthe telegraphy pulses are supplied via a biased diode to produce theswitching voltage.

Preferably, a bias source, normally cutting olf the switch tube, and agrid-current limiting resistor are connected in series with the inputresistor in the controlcircuit of the switch tube.

In order that the invention may be readily carried into elect, it willnow be described with reference to the accompanying drawing in which aradio-transmitter according thereto is shown partly in detail.

In the drawing, the reference numeral 1 denotes a crystal-controlledgenerator whereof the output voltage is applied via afrequency-multiplication stage 2 to the suppressor grid of a pentode 3acting as a mixer tube. Coupled to the control-grid of said pentode is ahighfrequency generator 4 which is tuned to a comparatively lowfrequency and whose output frequency is shifted by means of a variablereactance 5 in accordance with the telegraphy pulses delivered to theinput terminal 6.

The anode of the mixer tube 3 is coupled via a bandpass lter 7 to thecontrol-grid circuit of a pentode amplifier 8. The amplified voltage istaken from a tuned anode circuit 9 of said tube and supplied through acoupling capacitor 10 to a transmitter output stage 12 connected to anantenna 11.

The transmitter so far described is normally blocked by means of thescreen grids of the pentodes 3 and 8. In the absence of telegraphypulses to be transmitted, said screen-grids are earthed via a switchcontact a1.

The telegraphy pulses delivered to the input terminals 6 are supplied tothe variable reactance 5 and, by way of a lead 13, to a triode 14. Thecontrol-grid of said triode is connected to the cathode through agrid-resistor so that the triode is normally conductive and passescurrent via an anode resistor 16.

Connected to the anode of the triode 14 is the anode of a diode 17whereof the cathode is connected to earth via a resistor 18 and apotentiometer resistor 19. The cathode of the diode 17 is connected alsothrough a gridcurrent limiting resistor 20, tothe control grid of atriode "ice 2, 21 acting as a switch tube; The cathodeA ofv switch tube21 is connected tor the potentivorrreter resistor 19 through a cathoderesistor 22; They resistors 22' and 19 together with a further resistorzconstitute a potentiometer which is connectedv to" theanode voltageconductor. They anf- 'de' circuit of switch trioden 21' comprises a'quick-acting relay A wliic'li operates the aforesaid contact al'included in the screenagridr circuits of the transmittertubes and 8.

Failing telegraphy pulses across the' inputgt'erminal. 6x, thetrio`de`14- is conductive and: the anode of: the diode 17, which anodeisv coxmectecr tothe anoder of said triode; attains acomparatively low-potentials The potentials of the cathode of the diode 17 is determinedby the voltage set up` across the potentiometer resistor` 19,: which'voltage isf chosen to bel lnfgh (say -F'- v.)f so that`A the diode 1.7is eut ott when:` the ,triode/1.4 is conductive: Under these conditionsthe Z1 is' c'ut off by the voltage set up across the cathode resistor22;` Withf the triode 21 cut off the relay A provided in thev anodecircu-it is not energised and the closed circuit: Contact a1:- is= inthe position shown#y in` the drawing'.

When telegraph-y pulses of negative sign aref `delivered to the inputterminals 6; the triod'e1f4f is cut. off' inthe rhythm# of the pulses tobe transmittedr and' thel telegraphy pulses appear,r` after having.'amplified(y with` positive sign at the anode of the triode 14. Thepositive pulses appearing at the anode have an amplitude appreciablyexceeding the cut off bias of the diode 17 with the result that thetelegraphy pulses occur with positive sign across the resistor 18. Thisresistor 18 constitutes the input resistor of the control-grid circuitof the switch triode 21 which is released on the occurrence of atelegraphy pulse racross the resistor 18. Connected in parallel with theinput resistor 18 is the series-combination of a series resistor 24 anda holding capacitor 25. On the occurrence of a telegraphy pulse acrossthe input resistor 18 the holding capacitor 25 becomes comparativelyrapidly charged through the series resistor 24 which has a value ofresistance that is comparatively low as compared with the input resistor18. The series resistor 24 slightly delays the initial charging of thecapacitor 2S so that the leading edge of the first telegraphy pulsequickly renders the switch tube 21 conductive. In the interval betweentwo telegraphy pulses to be transmitted, the diode 17 is again cut oiand no voltage drop occurs on account of a current flowing through theresistor 16 and the diode 17. In this case, however, the voltage acrossthe holding capacitor 25 brings about a discharge current of saidcapacitor through resisto-rs 24 and 18 with the result that, since theresistor 24 is low relative to the resistor 18, practically the -fullvoltage of the capacitor 25 occurs across the resistor 18. In thismanner the switch triode 21 is prevented from being cut o in theinterval between two successive pulses of a train of telegraphy pulsesto be transmitted.

Hence, during the occurrence of a series of telegraphy pulses to betransmitted, the switch triode 21 is continuously conductive and therelay A is energised, thus actuating the closed circuit contact a1 withthe eiect that the screen-grids of the transmitter tubes 3 and 8 areconnected via a screen-grid resistor 26 to the anode-voltage conductorand the transmitter tubes 3 and 8 are released.

Upon termination of a series of telegraphy pulses thecircuit-arrangement resumes its initial condition in a retarded mannerin order to prevent the transmitter from becoming disengaged during ashort pause in a series of telegraphy pulses to be transmitted. In thecircuit-ar- 3 rangement shownin the drawing said delay in disengagementis obtainable in a simple manner bya suitable choice of the dischargeconstant of the holding capacitor 25.

In the present circuit-arrangement the main parts have the followingappropriate values:

The operating time of the quick-acting relay A is approximately 1millisecond.

In this circuit-arrangement the quick connection and retardeddisconnection referred to hereinbefore are also obtainable if partA ofthe input resistor 18'is used as a series resistor 24. v

With said values of the component parts 'the delay in disconnecting thetransmitter, which delay is mainly caused by the holding capacitor,amounts to w'ell above 200 milliseconds, which is suiicient to preventdisconnection of the transmitter during the transmission of atelegraphic dispatch.

What is claimed is: i

A radio transmitter for frequency-shift t'elegraphy, comprising atransmitter stage, a source of telegraph signals connected as an inputsignal to said transmitter stage, and a switching device connected tonormally block said transmitter stage, said switching device comprisinga grid- 4 controlled switch tube having a cathode and having an outputelectrode connected to control the blocking of said transmitter stage,means for biasing said tube to normally block said transmitter stage, aswitch-voltage generator circuit connected between the grid and cathodeof said switch tube and comprising an input resistor for said grid and aseries combination of a series resistor and a capacitor, said seriescombination being connected in parallel with said input resistor, andmeans including a biased diode connected to feed said telegraph signalsto said switch-voltage generator whereby said capacitor becomes chargedby said signals thereby to bias said tube so as to render saidtransmitter stage operative and whereby siad series resistor delays theinitial charging of said vcapacitor so that the leading `edge of the'rst of said telegraph signals quickly renders said switch tubeconductive,

said series resistor having a smaller value of resistance than saidinput resistor, and said capacitor and resistors having a time constantsuiciently large to cause said transmitter stage to remain operativeduring normal pauses between said telegraph signals.

References Cited in the le of this patent' UNITED STATES PATENTS2,232,080 Seidelbach Feb. 18, 1941 2,259,532 Nicholson Oct. 21, 19412,287,862 Brian .Tulle 30, 1942 2,372,005 Kinsman Mar. 20, 19452,549,873 Williams Apr. 24, 1951 2,730,617 Marmont et a1. Ian. 10, 19562,738,381 Miner Mar. 13, 1956

